Nickel-metal hydride battery using nanocrystalline TiFe-type hydrogen storage alloys

Mechanical alloying (MA) process was used to synthesize nanocrystalline TiFe-type alloys. XRD analysis showed that, firstly, after 20 h of milling, the starting mixture of the elements had transformed into an amorphous phase and, secondly, the annealing in high purity argon at 700 degrees C for 0.5 h led to formation of the CsCl-type structures with crystallite sizes of about 30 nm. It was found that the respective replacement of Fe in TiFe by Ni and/or by Al and Cr improved both the discharge capacity and the cycle life of these electrodes. In the nanocrystalline TiFe0.125Cr0.125Ni0.75 powder discharge capacity up to 154 mA h g(-1) was measured (at 40 mA g(-1) discharge current). Some of the produced nanomaterials were used as negative electrodes in sealed Ni/MH button cells. The results show that the sealed battery using the nanocrystalline TiFe0.25Ni0.75 or TiFe0.3Ni0.5Co0.2Zr0.05 alloys have about 1.5 times the capacity of the TiFe one. (c) 2005 Published by Elsevier B.V.